/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.config;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.BeanInitializationException;
import org.springframework.context.ApplicationContext;
import org.springframework.core.Ordered;
import org.springframework.lang.Nullable;
import org.springframework.util.ObjectUtils;
import org.springframework.web.reactive.result.view.HttpMessageWriterView;
import org.springframework.web.reactive.result.view.UrlBasedViewResolver;
import org.springframework.web.reactive.result.view.View;
import org.springframework.web.reactive.result.view.ViewResolver;
import org.springframework.web.reactive.result.view.freemarker.FreeMarkerConfigurer;
import org.springframework.web.reactive.result.view.freemarker.FreeMarkerViewResolver;
import org.springframework.web.reactive.result.view.script.ScriptTemplateConfigurer;
import org.springframework.web.reactive.result.view.script.ScriptTemplateViewResolver;

/**
 * Assist with the configuration of a chain of {@link ViewResolver}'s supporting
 * different template mechanisms.
 *
 * <p>In addition, you can also configure {@link #defaultViews(View...)
 * defaultViews} for rendering according to the requested content type, e.g.
 * JSON, XML, etc.
 *
 * @author Rossen Stoyanchev
 * @author Sebastien Deleuze
 * @since 5.0
 */
public class ViewResolverRegistry {

    @Nullable
    private final ApplicationContext applicationContext;

    private final List<ViewResolver> viewResolvers = new ArrayList<>(4);

    private final List<View> defaultViews = new ArrayList<>(4);

    @Nullable
    private Integer order;


    public ViewResolverRegistry(@Nullable ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }


    /**
     * Register a {@code FreeMarkerViewResolver} with a ".ftl" suffix.
     * <p><strong>Note</strong> that you must also configure FreeMarker by
     * adding a {@link FreeMarkerConfigurer} bean.
     */
    public UrlBasedViewResolverRegistration freeMarker() {
        if (!checkBeanOfType(FreeMarkerConfigurer.class)) {
            throw new BeanInitializationException("In addition to a FreeMarker view resolver " +
                    "there must also be a single FreeMarkerConfig bean in this web application context " +
                    "(or its parent): FreeMarkerConfigurer is the usual implementation. " +
                    "This bean may be given any name.");
        }
        FreeMarkerRegistration registration = new FreeMarkerRegistration();
        UrlBasedViewResolver resolver = registration.getViewResolver();
        if (this.applicationContext != null) {
            resolver.setApplicationContext(this.applicationContext);
        }
        this.viewResolvers.add(resolver);
        return registration;
    }

    /**
     * Register a script template view resolver with an empty default view name prefix and suffix.
     * <p><strong>Note</strong> that you must also configure script templating by
     * adding a {@link ScriptTemplateConfigurer} bean.
     *
     * @since 5.0.4
     */
    public UrlBasedViewResolverRegistration scriptTemplate() {
        if (!checkBeanOfType(ScriptTemplateConfigurer.class)) {
            throw new BeanInitializationException("In addition to a script template view resolver " +
                    "there must also be a single ScriptTemplateConfig bean in this web application context " +
                    "(or its parent): ScriptTemplateConfigurer is the usual implementation. " +
                    "This bean may be given any name.");
        }
        ScriptRegistration registration = new ScriptRegistration();
        UrlBasedViewResolver resolver = registration.getViewResolver();
        if (this.applicationContext != null) {
            resolver.setApplicationContext(this.applicationContext);
        }
        this.viewResolvers.add(resolver);
        return registration;
    }

    /**
     * Register a {@link ViewResolver} bean instance. This may be useful to
     * configure a 3rd party resolver implementation or as an alternative to
     * other registration methods in this class when they don't expose some
     * more advanced property that needs to be set.
     */
    public void viewResolver(ViewResolver viewResolver) {
        this.viewResolvers.add(viewResolver);
    }

    /**
     * Set default views associated with any view name and selected based on the
     * best match for the requested content type.
     * <p>Use {@link HttpMessageWriterView
     * HttpMessageWriterView} to adapt and use any existing
     * {@code HttpMessageWriter} (e.g. JSON, XML) as a {@code View}.
     */
    public void defaultViews(View... defaultViews) {
        this.defaultViews.addAll(Arrays.asList(defaultViews));
    }

    /**
     * Whether any view resolvers have been registered.
     */
    public boolean hasRegistrations() {
        return (!this.viewResolvers.isEmpty());
    }

    /**
     * Set the order for the
     * {@link org.springframework.web.reactive.result.view.ViewResolutionResultHandler
     * ViewResolutionResultHandler}.
     * <p>By default this property is not set, which means the result handler is
     * ordered at {@link Ordered#LOWEST_PRECEDENCE}.
     */
    public void order(int order) {
        this.order = order;
    }


    private boolean checkBeanOfType(Class<?> beanType) {
        return (this.applicationContext == null ||
                !ObjectUtils.isEmpty(BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
                        this.applicationContext, beanType, false, false)));
    }

    protected int getOrder() {
        return (this.order != null ? this.order : Ordered.LOWEST_PRECEDENCE);
    }

    protected List<ViewResolver> getViewResolvers() {
        return this.viewResolvers;
    }

    protected List<View> getDefaultViews() {
        return this.defaultViews;
    }


    private static class FreeMarkerRegistration extends UrlBasedViewResolverRegistration {

        public FreeMarkerRegistration() {
            super(new FreeMarkerViewResolver());
            getViewResolver().setSuffix(".ftl");
        }
    }

    private static class ScriptRegistration extends UrlBasedViewResolverRegistration {

        public ScriptRegistration() {
            super(new ScriptTemplateViewResolver());
            getViewResolver();
        }
    }

}
